Torsional mems device

ABSTRACT

A torsional MEMS device is disclosed. The torsional MEMS device includes a support structure, a platform, and at least two hinges, which connects the platform to the support structure. The platform has an active area and a non-active area. A plurality of sacrificial elements is disposed in the non-active area. If the resonant frequency of the torsional MEMS device is less than a predetermined standard resonant frequency of the torsional MEMS device, at least one sacrificial element is removed to reduce the total mass of the torsional MEMS device, and so as to increase the resonant frequency of the torsional MEMS device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a torsional MEMS device, andparticularly, to a torsional MEMS device of adjustable resonantfrequency.

2. Description of the Prior Art

In the past years, MEMS devices have been developed for miniaturizationof mechanical devices. The MEMS devices are manufactured by processesused for forming integrated circuits. Typical MEMS devices, includingmicro-gears, micro-levers, and micro-valves, are operated in companywith related electrical circuits to form several devices, such asaccelerometers, pressure and chemical sensors, and actuators.

MEMS devices are formed using silicon as material. The silicon materialsare processed by several semiconductor processes to form the structuresof the MEMS devices. For example, torsional MEMS devices use hinge asthe motive structure. The figure of the hinge is a major factor fordetermining the resonant frequency of the torsional MEMS devices. Inaddition, resonant frequency is also a major factor for determining theperformance of the torsional MEMS device. Therefore, several processesare performed to manufacture the hinge and to modify the hinge havingdesirable resonant frequency. It is appreciated that demands of theresonant frequency of the torsional MEMS device is getting moreaccurate, and it is getting difficult to form the hinge of determinedshape by a simple lithography process or an etch process at present. Asa result, applicant provides a torsional MEMS device which the resonantfrequency of the torsional MEMS device may be adjusted to overcome thelimitation resulted from the present processes for forming theconventional torsional MEMS devices. Additionally, the resonantfrequency of the torsional MEMS device of the present invention may beadjusted after the manufacturing processes to fulfill the standardresonant frequency of the product.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present invention to providea torsional MEMS device and the method of modulating the resonantfrequency of the torsional MEMS device for fulfilling the requirement ofproviding advanced products.

According to the present invention, a torsional MEMS device having asupport structure, a platform, and at least two hinges is provided. Thesupport structure has a space where the platform is placed. The platformand the support structure are connected by the hinges, which arearranged along a first direction that passes through the mass center ofthe platform. The platform includes an active area and a non-activearea, and a plurality of sacrificial elements disposed in the non-activearea, in which the sacrificial elements are used for modulating theresonant frequency of the torsional MEMS device.

According to the present invention, a method of modulating the resonantfrequency of a torsional MEMS device is disclosed. A torsional MEMSdevice having a support structure, a platform, and at least two hingesconnecting the support structure and the platform is provided. Theplatform includes an active area and a non-active area, wherein aplurality of sacrificial elements is disposed in the non-active area. Aresonant frequency test is performed to measure a raw resonant frequencyof the torsional MEMS device, and then the raw resonant frequency iscompared to a standard resonant frequency. If the raw resonant frequencyis less than the standard resonant frequency, at least one sacrificialelement is removed from the torsional MEMS device for reducing the massof the torsional MEMS device, and so that the raw resonant frequency ismodulated approaching to the standard resonant frequency.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 are schematic diagrams illustrating a torsional MEMSdevice according to a preferred embodiment of the present invention.

FIG. 3 is a flow diagram of a method for modulating the resonantfrequency of the torsional MEMS device according to a preferredembodiment of the present invention.

FIG. 4 shows a portion of the sacrificial elements are removed from theplatform for modulating the resonant frequency of the torsional MEMSdevice.

FIG. 5 and FIG. 6 are schematic diagram of a torsional MEMS deviceaccording to another preferred embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of this application. Thedrawings show, by way of illustration, specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are schematicdiagrams illustrating a torsional MEMS device according to a preferredembodiment of the present invention. As shown in FIG. 1, a torsionalMEMS device 10 having a platform 12 and two hinges 14 is provided. Thehinges 14 are arranged along a first direction passing through the masscenter of the platform 12, and are connected between the platform 14 anda support structure 16. The platform 12 is positioned in a space 18 ofthe support structure 16. The platform 12 is oscillated in the space 18using the hinge 14 as the resonant axis.

An active area 20 and a non-active area 22 are positioned on a frontsurface of the platform 12. In the present embodiment, the non-activearea 22 is disposed around the active area 20. A deposition process isperformed to form a metal layer on the active area 20, including Ti/Au,Cr/Au, or Al, or a visible coating that the metal layer or the visiblecoating layer reflects light and acts as a mirror. A device or acomponent may be placed in the active area 20, such as a mirror 26 shownin the present embodiment, but is not limited to it. A MEMS device or anelectrical circuit may also be placed in the active area 20 depending onthe requirement of the product. Please refer to FIG. 1 in company withFIG. 2. The platform 18 further has a plurality of sacrificial elements24 disposed in the non-active area 22. Each sacrificial element 24includes a sacrificial mass 241 and at least a connecting bar. Forexample, four connecting bars 242 are used to connect the sacrificialmass 241 to the platform 18 of the present invention. The connectingbars 242 are used to stably bond the sacrificial mass 241 to theplatform 18 without leading to extra torque during oscillation of theplatform 18. In addition, the connected bars 242 also preventsacrificial mass 241 from oscillating in a different resonant frequencyfrom that of the platform 18. In addition, the number of the connectingbars 242 may be modified during the manufacturing processes of thetorsional MEMS device 10, and the number of the connecting bars 242 isnot limited to the present embodiment.

Please refer to FIG. 3, which is a flow diagram of a method formodulating the resonant frequency of the torsional MEMS device accordingto a preferred embodiment of the present invention. The method ofmodulating the resonant frequency of the torsional MEMS device isperformed after the manufacturing process of the torsional MEMS device.The method of modulating the resonant frequency of the torsional MEMSdevice is shown as follows.

Step 100: A torsional MEMS device is provided. The torsional MEMS deviceincludes a support structure, a platform, and at least two hingesconnecting the platform to the support structure. The platform has anactive area, a non-active area, and a plurality of sacrificial elementsdisposed in the non-active area.

Step 102: A resonant frequency test is performed. A driving force isprovided during the resonant frequency test to make the torsional MEMSdevice oscillate and to measure a raw resonant frequency of the hinge.

Step 104: The raw resonant frequency of the torsional MEMS device iscompared to a standard resonant frequency to make sure of the rawresonant frequency match the range of the resonant frequency. Thestandard resonant frequency of the torsional MEMS device is determineddepending on the product having the torsional MEMS device of the presentinvention therein.

If the raw resonant frequency of the torsional MEMS device is out of therange of the standard resonant frequency, for instance, the raw resonantfrequency is less than the standard resonant frequency, Step 106 issubsequently performed.

Step 106: At least one sacrificial element 24 is removed to modulate theresonant frequency, better with the symmetric sacrificial elementremoving for the mass balance consideration to the platform 12,approaching to the standard resonant frequency. As shown in FIG. 4, thesacrificial mass 241 is removed from the non-active area 22 of thetorsional MEMS device 10 using a laser or using external force or energyto break the connecting bars 242. Therefore, a hollow 50 is formed afterthe sacrificial element 24 is removed. As a result, the total mass ofthe torsional MEMS device 10 is reduced and therefore the raw resonantfrequency is increased.

On the other hand, if the raw resonant frequency matches the standardresonant frequency, Step 108 is performed subsequently.

Step 108: The torsional MEMS device is transferred for the followingprocesses, such as packaging or combining with other elements, formanufacturing electronic products having the torsional MEMS devicetherein.

During above-mentioned method, the driving force for oscillating thetorsional MEMS device includes electromagnetic force, electrostaticforce, heat, or piezoelectric force. The torsional MEMS device of thepresent invention may comprise a corresponding device depending on thedriving force used for oscillation. For example, electromagnetic forceis used for oscillating the torsional MEMS device of the presentinvention. A magnetic material disposed on a back surface of torsionalMEMS device interacts with electromagnetic force generated by externalmetal coil, i.e., electromagnetic coil with the electrical control. Theexternal metal coil is located under the magnetic material. Theinteraction between magnet material and electromagnetic force generatedby the metal coil oscillates the torsional MEMS device. The magneticmaterial may be assembled to the torsional MEMS device after themanufacturing process of the torsional MEMS device is finished, or mayuse deposition or electroplating process to process the metal withmagnetic property on the desired area of the back surface of thetorsional MEMS device.

Please refer to FIG. 5 and FIG. 6, which are schematic diagram of atorsional MEMS device 30 according to another preferred embodiment ofthe present invention. The torsional MEMS device 30 having a supportstructure 36, a platform 32 and at least two hinges 34 is provided. Thehinges 34 are arranged along a first direction passing through the masscenter of the platform 32, and are connected between the platform 32 andthe support structure 36. The platform 32 is positioned in a space 38 ofthe support structure 36. The platform 32 is oscillated in the space 38using the hinge 34 as the resonant axis. An active area 40 and anon-active area 42 are positioned on a front surface of the platform 32.A plurality of sacrificial elements 44 disposed in the non-active area42. Each sacrificial element 44 includes a sacrificial mass 441 and atleast a connecting bar. For example, four connecting bars 442 are usedto connect the sacrificial mass 441 to the platform 32 of the presentinvention. The shape of the sacrificial element 44 of the presentembodiment is modified as a round-shaped sacrificial element in contrastto the rectangular-shaped sacrificial element 24 of the priorembodiment. The function of the sacrificial element is to change themass of the torsional MEMS device for modulating the resonant frequencyand is affected by the shape of the sacrificial elements. Furthermore,the position, the connecting relationship, and the function of thecomponents of the torsional MEMS device 30 are similar to those of thetorsional MEMS device 10. Detailed description of these components isillustrated in the prior embodiment.

The torsional MEMS device of the present invention may be manufacturedby a series of semiconductor processes, such as a lithography process,an etch process, a grinding process, and a CMP process. The pattern ofthe platform, the hinges, and the sacrificial elements may be defined onthe silicon wafers by the same mask. When the torsional MEMS device isformed on a wafer, it can be measured the resonant frequency. If thetorsional MEMS device is formed on a normal wafer, which has a pluralityof the same torsional MEMS device thereon, and has free space for itsfree torsion, which means that the torsional MEMS device is suspendingwithout constraint on the wafer, the resonant frequency measurement andresonant frequency modulation of the torsional MEMS devices formed on anormal wafer are performed in a wafer-level scale. The raw resonantfrequency of the respective torsional MEMS device may be modulatedindividually but the wafer still keeps as the wafer-level scale. Whenthe torsional MEMS device is formed on a thin wafer and there is no freespace for the torsional MEMS device to resonate, which means that thetorsional MEMS device is fixed on the wafer even after etch throughprocess, the resonant frequency of the hinge of the torsional MEMSdevice may be measured and modulated after these devices are dividedindividually. In other words, each torsional MEMS device is measured andmodulated in a chip-level scale.

In conclusion, the present invention provides a torsional MEMS devicecapable of modulating the resonant frequency thereof. After the resonantfrequency test is performed, the raw resonant frequency is compared tothe standard resonant frequency. If the raw resonant frequency is lessthan the standard resonant frequency, at least one sacrificial elementis removed depending on the position of the sacrificial element and thebalance of the platform. Laser or an external force is used to break theconnecting bars and subsequently the sacrificial element is removed.Accordingly, the total mass of the torsional MEMS device is reduced andthe resonant frequency is increased. The abnormal torsional MEMS deviceis prevented from scrapping after the removal of the sacrificialelement, and therefore, the yield of the product is increased.Furthermore, the position of the sacrificial elements is not limited tothe preferred embodiments of the present invention. The sacrificialelements may be disposed in a place on the platform without hinderingthe performance of the devices disposed in the active area. The devicedisposed in the active area is not limited to the mirror shown in thepresent embodiments. Mechanical structures, sensors, or electricalcircuits may be disposed in the active area depending on the finalproduct having the torsional MEMS device therein.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

1. A torsional MEMS device, comprising: a support structure having aspace therein; a platform disposed in the space, the platform includingan active area and a non-active area, wherein a plurality of sacrificialelements is disposed in the non-active area; and at least two hingesconnecting the platform and the support structure, the hinges beingarranged along a first direction which is passed through the center ofthe mass of the platform.
 2. The torsional MEMS device of claim 1,wherein the sacrificial elements is removable from the non-active areaof the platform.
 3. The torsional MEMS device of claim 1, wherein eachof the sacrificial elements comprises a sacrificial body and at least aconnecting bar connecting the sacrificial body and the platform.
 4. Thetorsional MEMS device of claim 1, wherein the non-active area ispositioned around the active area.
 5. The torsional MEMS device of claim1, wherein the platform further comprises a mirror disposed in theactive area.
 6. A method of modulating the resonant frequency of atorsional MEMS device, comprising: providing a torsional MEMS device,the torsional MEMS device comprising a support structure, a platform,and at least two hinges connecting the support structure and theplatform, in which the platform comprises an active area and anon-active area, wherein a plurality of sacrificial elements is disposedin the non-active area; performing a resonant frequency test to measurea raw resonant frequency of the torsional MEMS device, and comparing theraw resonant frequency to a standard resonant frequency; and removing atleast one sacrificial element from the torsional MEMS device if the rawresonant frequency is less than the standard resonant frequency tomodulate the raw resonant frequency approaching to the standard resonantfrequency.
 7. The method of claim 6, wherein each of the sacrificialelements comprises a sacrificial body and at least a connecting barconnecting the sacrificial body and the platform.
 8. The method of claim7, wherein the step of removing the sacrificial layer is performed byusing a laser to melt the connecting bar for removing the sacrificialbody from the non-active area of the torsional MEMS device.
 9. Themethod of claim 7, wherein the step of removing the sacrificial layer isperformed by using an external force to break connecting bar forremoving the sacrificial body from the non-active area of the torsionalMEMS device.
 10. The method of claim 6, wherein the platform oscillatesalong the hinges, which is the resonant axis of the platform.
 11. Themethod of claim 6, wherein the non-active area is positioned around theactive area.
 12. The method of claim 6, wherein the platform furthercomprises a mirror disposed in the active area.
 13. The method of claim6, wherein the torsional MEMS device is formed on a normal wafer, whichcomprises a plurality of torsional MEMS device, and the measurement andthe modulation of the raw resonant frequency of the raw resonantfrequency of the torsional MEMS devices are performed in a wafer-levelscale.
 14. The method of claim 6, wherein the torsional MEMS device isformed on a thin wafer, which comprises a plurality of torsional MEMSdevice, and the measurement and the modulation of the raw resonantfrequency of the raw resonant frequency of the torsional MEMS device areperformed in a chip-level scale.
 15. The method of claim 6, wherein thesacrificial element is removed symmetrically for maintaining the massbalance of the platform.